Fast Pyrolysis Oil Upgrading via HDO with Fe-Promoted Nb2O5-Supported Pd-Based Catalysts

Abstract

Due to the high acid, oxygen and water contents of fast pyrolysis oil, it requires the improvement of its fuel properties by further upgrading, such as catalytic hydrodeoxygenation (HDO). In this study, Nb2O5 was evaluated as a support of Pd-based catalysts for HDO of fast pyrolysis oil. A Pd/SiO2 catalyst was used as a reference. Additionally, the impact of iron as a promoter in two different loadings was investigated. The activity of the synthesized catalysts was evaluated in terms of H2 uptake and composition of the upgraded products (gas phase, upgraded oil and aqueous phase) through elemental analysis, Karl Fischer titration, GC-MS/FID and 1H-NMR. In comparison to SiO2, due to its acid sites, Nb2O5 enhanced the catalyst activity towards hydrogenolysis and hydrogenation, confirmed by the increased water formation during HDO and a higher content of hydrogen and aliphatic protons in the upgraded oil. Consequently, the upgraded oil with Nb2O5 had a lower average molecular weight and was therefore less viscous than the oil obtained with SiO2. When applied as a promoter, Fe enhanced hydrogenation and hydrogenolysis, although it slightly decreased the acidity of the support, owing to its oxophilic nature, leading to the highest deoxygenation degree (42.5 wt.%) and the highest product HHV (28.2 MJ/kg).

Investigation of Nb2O5 and Its Polymorphs as Catalyst Supports for Pyrolysis Oil Upgrading through Hydrodeoxygenation

“…Generated gases during HDO for the different catalysts and in the absence of a catalyst. Data from Pd/SiO 2 were taken from Campos Fraga et al …”

“…The dependence of the polymerization extension of the catalyst activity was clearly visible through blank experiment. Although it resulted in a decrease of oxygen, this decrease happened at the expenses of a stone-like char product . When using low-activity catalysts, the enhanced polymerized product tends to accumulate on the catalyst surface and further reduce its activity, in a cascade effect.…”

“…Oxygen removal mechanisms during the HDO: hydrogenolysis, gas formation, and organic oxygenated compounds in the aqueous phase. Data from Pd/SiO 2 were taken from Campos Fraga et al …”

“…(a) Weight distribution and percentage of compounds detected, (b) nonaromatic compounds, (c) aromatic compounds, (d) other compounds. Data from Pd/SiO 2 were taken from Campos Fraga et al…”

“…Nb 2 O 5 as a support for Pd, Ru, Co, and Ni has led to a remarkable increase in activity, selectivity, and stability in comparison to reference supports. In a previous study from our group, the application of Nb 2 O 5 as a catalyst support for bio-oil HDO has been demonstrated …”